1. Technical Field
The present invention belongs to the field of animal health and relates to nucleic acid sequences comprising the complete genome sequences of the genome segments of an infectious Schmallenberg virus. The invention also relates to the use of the nucleic acid sequences for producing infectious Schmallenberg virus to study the viremia and clinical symptoms induced by Schmallenberg virus in ruminants, and in the development of vaccines, therapeutics and diagnostics for the prophylaxis, treatment and diagnosis of a Schmallenberg virus infection.
2. Background Information
A novel orthobunyavirus, the Schmallenberg virus (SBV), was discovered in Europe in November 2011. After the first detection, the reported cases of SBV in sheep, cattle, and goats dramatically accumulated in several European countries to several thousand cases of PCR-positive malformed lambs and calves (1, 2). The virus was detected by metagenomics at the Friedrich-Loeffler-Institut (ELI) in samples of cattle with milk drop and fever. The investigated samples were collected in a farm near the city of Schmallenberg (North Rhine-Westphalia, Germany), and consequently the virus was named Schmallenberg virus (SBV). SBV is a member of the genus Orthobunyavirus within the family Bunyaviridae. It is related to the so-called Simbu serogroup viruses (1). SBV is like Akabane virus (AKAV) able to cross the placental barrier in pregnant cows and sheep, infect the fetus and cause fatal congenital defects during a susceptible stage in pregnancy (2). Therefore, SBV is a serious threat to ruminant livestock in Europe since vaccines are currently not available.
Orthobunyaviruses have a segmented, negative stranded RNA genome and are mainly transmitted by insect vectors like midges and mosquitis. The three segments (S, M and L) of the Orthobunyavirus genome allow genetic reassortment, which naturally occurs resulting in the emergence of viruses with new biological properties (3). The largest segment L encodes the RNA-dependent RNA polymerase. The M-segments encodes the viral surface glycoproteins Gn and Gc which are responsible for cell fusion, viral attachment and the induction of neutralizing antibodies. The small S-segment encodes the nucleocapsid N which is also involved in complement fixation (4). The relationship between Orthobunyaviruses were often only determined by serological cross-reactivity (5). In the era of DNA sequencing, phylogenetics has additionally been assessed by comparison of partial genome sequences (full N and partial Gc gene) (6). Therefore, available and published genome sequence information of full-length genomes is sparse. As a consequence, in-depth phylogenetic analyses are difficult. In conclusion, a detailed and reliable taxonomic classification of SBV could not be made. Preliminary investigations showed similarities of the M- and L-segment sequences to partial AKAV and Aino virus (AINOV) sequences. The N gene was most closely related to Shamonda virus (SHAV) (1).
SBV was the first orthobunyavirus of the Simbu serogroup detected in Europe. The virus is apparently transmitted by arthropod vectors. Biting midges probably play an important role in transmission. According to the current state of knowledge, ruminants are susceptible to infection with SBV. Adult animals may develop mild disease, if any. However, transplacental infection occurs frequently and can lead to severe congenital malformation of the vertebral column (Kyphosis, lordosis, scoliosis, torticollis) and of the scull (macrocephaly, brachygnathia inferior) as well as variable malformations of the brain (hydrancenphaly, porencephaly, cerebellar hypoplasia, hypoplasia of the brain stem) and of the spinal cord in lambs, kids and calves. The infection spread rapidly over large parts of North Western Europe. Belgium, Germany, France, Italy, Luxembourg, the Netherlands, Spain and the United Kingdom have been affected so far.
The Simbu serogroup, named according to the prototype virus, is the largest serogroup of Orthobunyavirus and contains at least 25 viruses, among them medically important viruses such as Akabane virus, Oropouche virus, Sathuperi virus or Douglas virus, most of which can cause malformations in new born ruminants, but also human beings can be affected. Akabane virus, for instance, causes congenital defects in ruminants and circulates in Asia, Oceania and Africa, whereas Oropouche virus is responsible for large epidemics of Oropouche fever, a zoonosis similar to dengue fever, in human populations in South Africa. Sathuperi virus has lent his name to the Sathuperi serogroup, to which belong also Douglas virus and SBV.
Reverse genetic systems for Bunya viruses are technically challenging, which is reflected by a small number of publicated systems. For Orthobunyaviruses a minigenome system (7), a transcription and replication competent trVLP (virus like particle) system (8) and full-length clone systems (9, 10) have been described. However, although the rescue system to recover infectious Bunyamvera virus of the Group C serogroup (genus Orthobunyavirus) entirely from cloned cDNA, that uses T7 RNA Polymerase has already been described in 1996 (9, 10), and comparable system exists for a Simbu serogroupe virus. One rescue system, which is based on cloned cDNAs but utilizes RNA polymerase I for the production of viral transcripts, had been described for Akabane virus, so far. However, there is a strong need for reverse genetic systems, particularly with regard to T7 RNA polymerase-driven systems allowing to produce infectious Schmallenberg viruses, for a better understanding of the diseases induced by said virus, for reproducing said disease in its different forms, for comparative tests, and as platform for the development of new vaccines, medications and diagnostics for the prophylaxis, treatment and diagnosis of viremia and diseases caused by SBV.